Can't animate the scale of objects changing
You need to insert keyframes for changes to values.

Go to frame one, scale the object to 0.001 and with the mouse cursor in the 3d view press I > Scale. Now all frames will have this value. 
If you change to frame 20 and scale it to 200, you will notice the scale property being orange. Orange means that this value is different than the keyframed one and will be lost after changing frames.

Press I > Scale again to insert another keyframe for this value.